X-ray ct apparatus

ABSTRACT

An X-ray CT apparatus is capable of obtaining an image of arbitrary size for an arbitrary part of an object to be examined. The X-ray CT apparatus prepares two-dimensional data and three-dimensional data from a plurality of X-ray information obtained by driving an X-ray tube and an X-ray information detector through one rotation around a patient in a range between a lower jaw and the eyes of the patient, and it displays a tomographic image based thereon on a display unit. A rotational mechanism is fitted to a support, a U-shaped arm is mounted on the support with the X-ray tube and the X-ray information inputting means facing each other and fitted, and the image of an arbitrary size of an arbitrary part of the patient is collected and displayed as the patient is supported in a chair which is capable of being electrically-driven in the vertical direction.

TECHNICAL FIELD

[0001] The present invention relates to an X-ray CT apparatus, whichradiates X-rays to a portion of an object to be examined and processes aprojection image thereof to create a tomogram; more particularly, theinvention relates to an X-ray CT apparatus which can create a tomogramon a portion of a patient which is undergoing dental care.

BACKGROUND OF THE INVENTION

[0002] In dental care, general imaging in which film is positioned inback of teeth to perform X-ray imaging, panoramic imaging which involvessimultaneously rotating an X-ray tube and film, cephalometric imaging inwhich an X-ray tube is greatly detached from the film during imaging,and the like are available. However, because all of these proceduresinvolve simple X-ray imaging, only a plane image is obtainable.

[0003] Recently, a new type of dental surgery has been performed inwhich an implant is embedded into bone to fix artificial teeth to thejaw. When such surgery is performed, it is important tothree-dimensionally observe the form of the teethridge and nearby bones.However, according to conventional X-ray imaging, it is impossible tothree-dimensionally observe the form of teethridge and nearby bones, andso the form has to be determined on the basis of a plane image toperform surgery. Accordingly, the surgery requires more than normalskill, and there has been a problem in that a medical accident is likelyto happen.

[0004] Such a problem can be solved by three-dimensionally observing theform of the teethridge and nearby bones using a conventional X-ray CTapparatus. The conventional X-ray CT apparatus does not image only oneportion of a section of a body, such as a teethridge and nearby bones,but radiates X-rays to the whole area and obtains a tomogram of adesired portion from the obtained whole-area image. However, because thedesired portion which forms the subject here is the form of theteethridge and the nearby bones, the image thereof becomes smallcompared with the entire image. Therefore, when the desired portion issmall, the extracted image is small, and it is difficult to be recognizedetails since the image thereof is extracted from the entire image.

[0005] In this case, a tomogram of the desired portion can be easilyimaged by constructing an X-ray CT apparatus which operates to radiateX-rays only to the desired portion and to create a projection imagethereof. One example of an apparatus which radiates X-rays only to adesired portion to create a CT image thereof is described in JapaneseUnexamined Patent Publication 2000-139902.

[0006] According to Japanese Unexamined Patent Publication 2000-139902,because X-rays are locally radiated to a local portion by using an X-raycone beam collimator, prevention of excessive radiation exposure of theobject is taken into consideration. However, in operations for selectingwhether a tomogram of one tooth being a lesion is created or that of awhole jaw is created, for example, the collimator of an X-ray generatorhas to be set in every imaging operation, which makes the selectingoperation complicated. Therefore, it is difficult to image an arbitraryportion of arbitrary size in an object. This problem is not taken intoconsideration at all in Japanese Unexamined Patent Publication2000-139902.

[0007] An object of the present invention is to provide an X-ray CTapparatus which can image an arbitrary portion of an arbitrary size inan object.

SUMMARY OF THE INVENTION

[0008] To achieve the above-stated object, an X-ray CT apparatusaccording to the invention includes: an X-ray generating means forgenerating X-rays; an X-ray detecting means arranged opposite to theX-ray generating means for two-dimensionally detecting a dose of X-rayspassing through an object to be examined; means for holding the X-raygenerating means and the X-ray detecting means so that the object isplaced therebetween; rotation driving means for driving the holdingmeans to rotate around the object; image processing means for producinga tomogram of the object on the basis of the X-ray dose detected by theX-ray detecting means; and display means for displaying the tomogram,further including means for changing the size of the field of view (FOV)in accordance with a detected portion of the object displayed on thedisplay means.

[0009] Specifically, if the FOV size is set for one tooth, a tomogram ofone tooth is created by image processing means from the X-ray dose basedon a one-tooth FOV size, and the tomogram is displayed by the displaymeans. If the FOV size is set for a whole jaw, a tomogram of the wholejaw is created by the image processing means from the X-ray dose basedon a whole-jaw FOV size, and the tomogram is displayed by the displaymeans. Thus, when the whole jaw or one tooth is imaged, an arbitraryportion of arbitrary size in the object can be imaged.

[0010] Further, the FOV size changing means includes X-ray convertingmeans for converting the X-rays into visible light; light receivingmeans for converting the visible light converted by the X-ray convertingmeans into electrical signals; and means for changing a portion of thevisible light of the X-ray converting means necessary for creating thetomogram.

[0011] This is involved with the specific structure of the X-raydetecting means, which includes X-ray converting means, such as an imageintensifier device, light receiving means, such as a CCD camera, and anoptical system which forms an image of the image intensifier device onthe CCD camera. The optical system includes an electric collimator foradjusting the amount of light. When various areas are imaged, theoptical system adjusts the size of the image and the brightness of theelectric collimator, thus an optimum CT image can be obtained.

[0012] Further, the X-ray detecting means is a two-dimensional X-rayflat sensor, and the FOV size changing means includes means for changingthe region necessary for creating the tomogram using electrical signalsconverted by the two-dimensional X-ray flat sensor.

[0013] This is involved with the specific structure of the X-raydetecting means, in which an two-dimensional X-ray flat sensor isemployed instead of the image intensifier and the CCD camera. Accordingthereto, even when various areas are imaged, the image size is adjustedby shutting off electrical signals of an unnecessary area and the imagebrightness displayed, while changing the amplification of thetwo-dimensional X-ray flat sensor elements, thereby an optimum CT imagecan be obtained.

[0014] The FOV size changing means includes means for inputting adesired FOV size by moving a cursor of a pointing device to an FOV sizechanging switch displayed on the display means and control means forchanging the FOV size to the size input by the input means. Thus, theinput of an FOV change can be certainly and promptly set by operatingthe FOV changing switch displayed on a monitor of the display means.

[0015] Further, by controlling the conditions of X-ray generation of theX-ray generating means in accordance with the FOV size designated by theFOV size changing means, an image of the input X-ray dose can beobtained under more preferable X-ray conditions of the X-ray detectingmeans changed due to the change of the FOV size, with adjustment of thetube voltage, the tube current, and the radiation time of the X-raygenerator.

[0016] Further, the apparatus includes means for adjusting the size ofthe tomogram displayed by the display means. Thus, a portion having anarbitrary size can be imaged.

[0017] Further, the adjusting means includes means for adjusting thedistance between the X-ray generating means and the X-ray detectingmeans on the holding means. Thus, since the radiation field of the X-raygenerating means is fixed, by properly adjusting the distance betweenthe X-ray generating means and the X-ray detecting means to bring themclose to or keep them away from each other, an arbitrary FOV size can befreely chosen. Therefore, the portion which needs to be examined by adoctor can be enlarged. By adjusting the distance in accordance with thesize of an element of the optical system or of the two-dimensional flatsensor, highly accurate adjustment can be carried out.

[0018] Further, the adjusting means is designed to adjust the distancebetween the X-ray generating means and the X-ray detecting means byextending and retracting a part of the holding means. Thus, when theX-ray generating means and the X-ray detecting means are mounted on thedistance adjusting means, the distance therebetween can be adjusted byextending and retracting a part of the distance adjusting means.

[0019] Further, the holding means has a U-shaped arm and is providedwith the X-ray generating means and the X-ray detecting means onopposite ends of the arm, and the rotation driving means is designed torotate the U-shaped arm around its intermediate portion. This isinvolved with the specific structure of the X-ray CT apparatus, in whichthe X-ray generating means and the X-ray detecting means arerespectively provided on the opposite ends of the U-shaped arm, andX-rays are radiated from the X-ray generating means to the X-raydetecting means between the ends of the U-shaped arm. The rotationdriving means rotates X-rays around the object by rotating the U-shapedarm around its intermediate portion, thus a fluoroscopic image necessaryfor creating a tomogram can be obtained.

[0020] Further, the apparatus includes means for extending a tomogram ofthe FOV size that has been changed by the FOV size changing means. Byswitching the FOV size, both the whole face and a single tooth can beenlarged in the image, whereby it becomes easy to formulate a treatmentplan for implant surgery and to observe a passage after the surgery.

[0021] The apparatus includes means for determining the position of theobject so that an arbitrary region of the object is located at therotation center of the X-ray generating means and the X-ray detectingmeans. When the object is a human body, it is necessary to finely adjustthe imaging position of the chair which supports the patient inaccordance with the difference of his/her seated height and the portionto be imaged. Here, the position can be freely determined in athree-dimensional space by electrically moving the object up and down,back and forth, and from side to side, or by rotating the patient.Further, when the head is imaged, the imaging position thereof can bedetermined by moving the head back and forth and from side to side or byrotating it in accordance with the shape thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a front view of a scanner mechanism unit of an X-ray CTapparatus according to one embodiment of the invention.

[0023]FIG. 2 is a left side view of FIG. 1.

[0024]FIG. 3 is a top view of FIG. 1.

[0025]FIG. 4 is a block diagram schematically showing the structure ofan X-ray CT apparatus according to one embodiment of the invention.

[0026]FIG. 5 is a diagram showing change in the appearance of an X-rayCT apparatus when a relatively large region is imaged.

BEST MODE FOR CARRYING OUT THE INVENTION

[0027] Hereinafter, a preferred embodiment of an X-ray CT apparatusaccording to the present invention will be described with reference tothe accompanying drawings. The X-ray CT apparatus according to theinvention includes a scanner mechanism unit 1 and an image processingunit 2. FIG. 1 shows the scanner mechanism unit 1 of the X-ray CTapparatus according to one embodiment of the invention.

[0028] The scanner mechanism unit 1 includes a column 11, a U-shapedsupport rotation driving unit 12, arms 131 and 132 that form theU-shaped support, X-ray generator 14, X-ray information inputting means(detector) 15, control means 16, a chair 17 for the patient, a console18, a chair driving device 19, and a mat switch 1A. The column 11 has areverse L shape and has the U-shaped support driving unit 12 mounted onend thereof. The U-shaped support driving unit 12 holds the suspendedarms 131 and 132 and rotates the arms 131 and 132 at a predeterminedspeed with respect to the end of the reverse L-shaped column 11, whichconstitutes a rotation center.

[0029] The X-ray generator 14 is designed to generate X-rays, and it isprovided on one end of the arm 131. The X-ray information detector 15 isarranged opposite to the X-ray generator 14, and it is mounted on oneend of the shaped arm 132. The detector 15 is designed totwo-dimensionally detect an X-ray dose passing through the object. Thatis, the X-ray generator 14 is arranged opposite to the X-ray informationdetector 15 in relation to the U-shaped support constituted by arms 131and 132. The U-shaped support constituted by arms 131 and 132 is drivento rotate by approximately 405 degrees around the end of the reverseL-shaped column 11, which constitutes the rotation center, by theU-shaped support rotation driving unit 12. Although the imaging range is360 degrees, the rotation range is set to be wider by 45 degrees so asto begin imaging from the point where the rotation speed becomesconstant.

[0030] Further, the arm 131 of the U-shaped support can be freelyextended and retracted in a radius direction by sliding inside the arm132, and thus the distance between the X-ray generator 14 and the X-rayinformation detector 15 is adjusted. FIG. 5 illustrates the state inwhich the arm 131 is extended to the maximum, and FIG. 1 illustrates thestate in which it is retracted to the maximum. After the beginning ofimaging, the X-ray generator 14 radiates X-rays in pulses in synchronismwith image collection to reduce the X-ray exposure. The timing thereofis controlled by a position detection encoder built in the U-shapedsupport rotation driving unit 12.

[0031] As seen in FIG. 4, the X-ray information detector 15 includes aCCD camera 151, an electric collimator 152, and an image intensifierdevice 153. The device 153 converts incident X-rays passing through theobject into visible light. The CCD camera 151 receives the visible lightconverted by the device 153 and converts it into electrical signals. TheX-ray information detector 15 can switch the imaging range in accordancewith the imaging portion. The optical system is constructed so that theFOV size is set to be small when teeth are imaged, and it is set to belarge when the jaw and face of a patient are imaged. By switching theFOV size, both the whole face and a single tooth can be enlarged in theimage, whereby it becomes easy to establish the treatment plane ofimplant surgery and observe passage after the surgery. That is, in theX-ray information detector 15, the pixel size of the CCD camera 151 ischanged by switching the FOV size of the image intensifier device 153using the optical system including the electric collimator 152, wherebyan FOV having a small size can be observed in detail.

[0032] The control device 16 for controlling the entire scannermechanism unit 1 is provided below the column 11. The control unit 16controls the X-ray conditions, the scanner mechanism unit 1, and theX-ray radiation according to control signals received from the imageprocessing unit 2. Meanwhile, instead of the image intensifier device153, an imaging plate, a two-dimensional flat X-ray sensor, and the likealso may be used. Here, if a two-dimensional flat X-ray detector isused, X-rays can be directly converted into electrical signals withoutpassing through a CCD camera or the like, which contributes to makingthe X-ray CT apparatus smaller and lighter.

[0033] When the FOV size is switched with the two-dimensional X-raysensor, each element arranged in a direction of X-ray input is in astate of being activated or inactivated, and X-ray data is not obtainedfrom the inactivated elements, but is obtained from the activatedelements.

[0034] The chair 17 is provided so that the head of the patient islocated on a rotation center axis of the U-shaped support constituted bythe arms 131 and 132. The chair 17 is attached to the side of the column4, including the chair driving device 19 for adjusting the imagingposition in response to a difference of seated heights of the patientand finely adjusting the imaging position in response to an imagingportion, which can be electrically moved freely in a three-dimensionalspace, i.e., up and down, back and forth, and from side to side.Further, the chair driving device 19 also can be moved in athree-dimensional space in X-, Y-, and Z-directions, and it can bedriven to rotate around the head of the patient as a rotation center.The chair includes a chair position detecting unit 171 for detecting theheight of its seat and a shoulder position detecting unit 172 fordetecting the position of the shoulders of the patient so that theshoulders do not touch the rotating X-ray information 15. The chairposition detecting unit 171 is not shown in FIG. 1 to FIG. 3. The chair17 is provided with a shoulder pad 173 and a head pad 174. The shoulderpad 173 includes a built-in shoulder position detecting unit 172.Further, the shoulder pad 173 is designed to rotate upward by 90 degreesso as not to hinder the patient sitting in the chair 17. Positionsignals detected by the chair position detecting unit 171 and theshoulder position detecting unit 172 are transmitted to the controldevice 16 and are signal-processed there. When the distance between theshoulder pad 173 and the X-ray information detector 15 is reduced, aninterlock is engaged so that the chair 17 cannot be lifted. The head pad174 has a band or the like for fixing the head of the patient duringimaging. Further, the position at which the head pad 173 is attached canbe moved back and forth and from side to side to move the imagingportion in accordance with the shape of the head. The mat switch 1A is amat provided so as to surround a rotating area 133 of the U-shapedsupport constituted by the arms 131 and 132. When a person or somethingsteps onto the mat switch 1A, it closes the interlock so that the arms131 and 132 cannot rotate.

[0035] The image processing unit 2, as seen in FIG. 4, includes theimage processing device 21, a CRT 22, a keyboard 23, a mouse 24, and apointing device, such as a trackball and a touch panel. The imageprocessing device 21 takes in 288 X-ray fluoroscopic images with a360-degree FOV, reconstructs those images into a two-dimensional image,and displays the two-dimensional image on the monitor (CRT) 22. Theimage reconstruction performed by the image processing device 21 is aknown technique of cone-beam CT, in which multiple vertical items ofinformation can be read in during one rotation of the U-shaped supportaround a patient. By starting 3D display software built in the imageprocessing device 21, a 3D image can be created and displayed on thebasis of the information. Because the shape can be three-dimensionallyunderstood, the image is useful in making a plan of implant surgery.

[0036] A method of switching the FOV size of this X-ray CT apparatuswill be described. First, a cursor is moved onto an FOV size changingswitch displayed on the monitor 22 by using the mouse 24. A selected FOVsize is communicated from the image processing device 21 to the controlunit 16. The control unit 16 outputs a change of X-ray conditions (tubevoltage and tube current) on the basis of the instructed FOV size. Also,the control unit 16 outputs a signal to the electric collimator 152 foradjusting an FOV size switching signal of the image intensifier device153 and the light amount of the CCD camera. In the image intensifierdevice 153, if the FOV size is reduced and the X-ray conditions are thesame as in a large FOV size, the light amount output to the CCD cameradecreases. Accordingly, the image displayed on the CRT becomes dark andits contrast is deteriorated. Therefore, it is necessary to improve theX-ray conditions and activate a collimator in the front of the CCDcamera in an opening direction to display an image having the samecontrast as that of a large FOV size.

[0037] More specifically, the setting of the FOV size changing switchbetween imaging of the shape of a whole jaw and imaging of a teethridgeand nearby bones of one tooth will be described. Here, the FOV size ofX-rays input into the image intensifier device 153 is set for the wholejaw, a tomogram of the whole jaw of the object is created by the imageprocessing device 21 from an X-ray dose based on a radiation area of thewhole jaw, and a tomogram of one tooth is displayed on the CRT 22.Further, the FOV size of X-rays input into the image intensifier device153 is set for one tooth, a tomogram of one tooth of the object iscreated, and the tomogram of one tooth is displayed on the CRT 22. Inthis manner, when the whole jaw and one tooth are sequentially imaged,the resolution is not deteriorated, and so an image contributing todiagnosis is obtainable.

[0038] In addition, while the radiation field of the X-ray generator 14is not moved, the X-ray generator 14 can be moved from the positionshown in FIG. 5 toward the image intensifier device 153 by electricallyor manually changing the arm length of the U-shaped supportedconstituted by the arms 131 and 132 to which the X-ray generator isattached, as shown in FIG. 1, and thus, an arbitrary FOV size can bechosen. Accordingly, a portion needed for the examination by a doctorcan be enlarged.

[0039] Further, to effect a change of the support length, a telescopicsystem utilizing a mechanism which changes the length of the support, asdescribed in Japanese Unexamined Patent Publication Hei. 8-112272, isemployed. If the system is electrically driven, a motor or the like isused. If the system is manually driven, an operator properly adjusts theextendable arm. The details of the mechanism are omitted here.

[0040] According to the above-described embodiment, by formingtwo-dimensional or three-dimensional data in an area from the lower jawto the eyes of a patient, an image can be displayed, and sothree-dimensional observation can be performed for evaluation of thelower jaw before surgery and following surgery. Therefore, a medicalaccident in implant surgery can be prevented and the diagnosticefficiency can be improved. Further, a panoramic image and acephalometric image obtained in conventional X-ray imaging also can bedisplayed and simultaneously used with a three-dimensional image,whereby a more accurate diagnosis can be conducted.

[0041] The above-described embodiment has been directed to the case ofusing an X-ray CT apparatus in which two-dimensional andthree-dimensional data in an area from the lower jaw to the eyes areformed, and a tomogram is created based on such data. However, it ispossible to similarly apply the embodiment to a conventional X-ray CTapparatus.

[0042] As described above, by using an X-ray CT apparatus according tothe present invention, an arbitrary portion of arbitrary size in apatient can be imaged.

1. An X-ray CT apparatus comprising: X-ray generating means forgenerating X-rays; X-ray detecting means arranged opposite to the X-raygenerating means for two-dimensionally detecting a dose of X-rayspassing through an object to be examined; means for holding the X-raygenerating means and the X-ray detecting means so that the object islocated therebetween; rotation driving means for driving the holdingmeans to rotate around the object; image processing means for producinga tomogram of the object based on the X-ray dose detected by the X-raydetecting means; and display means for displaying the tomogram, furthercomprising means for changing an FOV size of the X-ray detecting meansin accordance with a detected portion of the object displayed by thedisplay means.
 2. An X-ray CT apparatus according to claim 1, whereinthe FOV size changing means includes X-ray converting means forconverting the X-rays into visible light; light receiving means forconverting the visible light converted by the X-ray converting meansinto electrical signals; and means for changing a portion of the visiblelight converted by the X-ray converting means necessary for creating thetomogram.
 3. An X-ray CT apparatus according to claim 1, wherein theX-ray detecting means is a two-dimensional X-ray flat sensor forconverting X-rays into electrical signals, and the FOV size changingmeans includes means for changing a portion of the electrical signalsconverted by the two-dimensional X-ray flat sensor necessary forcreating the tomogram.
 4. An X-ray CT apparatus according to claim 1,wherein the FOV size changing means includes means for inputting adesired FOV size by moving a cursor of a pointing device onto an FOVsize changing switch displayed on the display means and control meansfor changing an FOV size to the size input by the inputting means.
 5. AnX-ray CT apparatus according to claim 1, further comprising means forcontrolling conditions of X-ray generation of the X-ray generating meansin accordance with the FOV size changed by the FOV size changing means.6. An X-ray CT apparatus according to claim 1, further comprising meansfor adjusting a size of the tomogram displayed by the display means. 7.An X-ray CT apparatus according to claim 6, wherein the adjusting meansincludes means for adjusting a distance between the X-ray generatingmeans and the X-ray detecting means on the holding means.
 8. An X-ray CTapparatus according to claim 6, wherein the adjusting means adjusts thedistance between the X-ray generating means and the X-ray detectingmeans by extending and retracting a part of the holding means.
 9. AnX-ray CT apparatus according to claim 6, wherein the holding means is aU-shaped arm provided with the X-ray generating means and the X-raydetecting means respectively on the ends, and the rotation driving meansrotates the holding means around an intermediate portion of the U-shapedarm being the center.
 10. An X-ray CT apparatus according to claim 6,further including means for expanding the tomogram obtained with the FOVsize changed by the FOV size changing means.
 11. An X-ray CT apparatusaccording to claim 1, further comprising means for determining aposition of the object so that an arbitrary portion of the object islocated on the rotation center of the X-ray generating means and theX-ray detecting means.